Help ID spindle!!

[71c10RDU]

Ok I’ve done a fair amount of research and I’m stumped. I bought my 71 c10 and it already had drop spindles on it. There are no part numbers or branding stamped on them. I’m about to order tubular upper and lower arms and I’m not sure which year these are. The outter tie rods suggest they are in fact for a 71-72. However the castle nuts for the upper ball joints thread up so far the cotter pin doesn’t engage the nut. 🤷🏻*♂️ I don’t want to order the wrong arms. All my research suggests if the tie rods fit then that’s the year of the spindle, but the ball joints suggest otherwise. Maybe they installed wrong ball joints or castle nuts?? Here’s a couple of pics of the ball joints.